A variety of heat exchangers, including an exhaust gas cooler for a vehicle such as an exhaust gas recirculation (EGR) cooler for recycling exhaust gas, a fuel cooler, an oil cooler, an intercooler, a superheater of a waste heat recovery system and a boiler, is used. Heat exchangers are configured to exchange heat between various types of fluid, such as gas-gas, liquid-gas and liquid-liquid. For instance, EGR can extract a portion of exhaust gas from an exhaust system of a diesel engine, circulate the extracted portion of exhaust gas through an intake system of the diesel engine, and add the extracted portion of exhaust gas to mixture gas, thereby reducing the production of nitrogen oxides (NOx). EGR can also realize many beneficial effects, such as a reduction in a pump loss, a reduction in the heat loss of coolant depending on the temperature drop of exhaust gas, an increase in a specific heat ratio depending on the amount of working gas and variations in composition, and resultant improvements in a cycle efficiency. Therefore, EGR is widely used as a method available for purifying exhaust gas and improving heat efficiency in a diesel engine.
Such a heat exchanger includes a heat exchanger housing through which fluid that is to be subjected to heat exchange passes and fin structures which are disposed inside the heat exchanger housing. The fin structures can improve the heat exchange efficiency of the fluid by inducing the fluid to become turbulent.
Such fin structures have a variety of shapes, such as a corrugated structure, a flat panel structure, a wave structure, or the like. Wave fin structures are recently popular considering their ability to improve heat exchange efficiency by promoting the tendency of fluid to become turbulent.
Wave fins are configured such that a plurality of hills and a plurality of valleys are repeatedly arranged in the transverse direction and are waved in the longitudinal direction, i.e. the direction in which fluid flows, thereby forming a plurality of partitioned fluid passages. This consequently allows the fluid that passes through the fluid passages of the wave fins to flow through the waved structure in the waved direction, thereby causing the fluid to become turbulent and circulate.
However, since the heat exchanger housing has a relatively small interior volume, there are several limitations against the ability of conventional wave fins to enhance the turbulence of fluid. In particular, since the surface of the conventional wave fins is smooth, the turbulent kinetic energy of fluid that passes through individual fluid passages is not substantially enhanced. In addition, a loss in kinetic energy occurs while fluid is flowing. Accordingly, the heat exchange efficiency of fluid is not substantially high, which is problematic.